1. Field of Invention
The present invention relates to a family of glasses that absorbs ultraviolet (UV) radiation and filters out yellow light in the visible region of the electromagnetic spectrum.
2. Description of Related Art
Ultraviolet (UV) radiation not only has harmful effects on human tissues, but can also cause degradation and discoloration in such items as paints, fabrics, and plastics. UV radiation covers wavelengths that range from approximately 60 nm to just short of 400 nm (xcx9c398 nm). The sun emits UV radiation, but it is not the only light source that emits UV waves. Various types of artificial lighting, such as halogen lamps and especially discharge and arc lamps, may also emit UV radiation. Accordingly, an interest in minimizing UV radiation emitted by artificial light sources has long existed. The transmission of UV radiation may be reduced, for example, by utilizing UV absorbing glass in the fabrication of lighting devices such as lamp envelopes, sleeves, reflectors, and lenses.
Equally as important as the interest in minimizing UV radiation emitted by artificial light sources is the interest in producing lighting devices having improved illumination and high color rendering. This interest is pursued especially zealously in the automotive industry where there is a push for vehicle headlight systems that can provide improved night visibility. One option is high-intensity discharge (HID) lamps which are usually found on luxury and high-end performance automobiles. Although, HID lamps offer improved brightness and night visibility, they are costly. Therefore, there exists an interest in providing less expensive lamps with similar performance properties. One method of achieving this objective is to approximate the illumination properties of HID lamps in less expensive light sources, such as tungsten halogen lamps or incandescent lamps. This may be achieved by employing lamp envelopes or lenses made of glass, which filters visible light, for example neodymium containing glass that raises the color temperature of halogen or incandescent light sources. This results in a light source having improved brightness, which can provide higher contrast definition to the illuminated objects.
Neodymium containing glass is known in the glass industry, and has historically found employment in the aviation and navigation fields. Neodymium, a rare-earth element, is most often incorporated in glass as an oxide, more specifically Nd2O3. Long known as a coloring agent, neodymium like the other rare-earth elements possesses an absorption spectra that extends over both the visible and invisible regions, transferring practically unchanged to base compounds, such as glasses. Neodymium absorbs light in the yellow region of the visible spectrum, between about 568 and 590 nm. As a result, light passing through neodymium containing glass accentuates the red and green tones in the surrounding environment. Experiments have also shown that neodymium-containing glass provides an increase in visibility during foggy weather. See, Weyl, Woldemar A, Coloured Glasses, published by Society of Glass Technology, xe2x80x9cThortonxe2x80x9d, 20 Hallam Gate Road, Sheffield, S10 5BT, England, 1951; pp. 218, 226, 227. The content of this reference is incorporated herein by reference.
Recently, neodymium containing glass has been proposed for the production of automobile headlights to reduce the visual discomfort from oncoming cars (U.S. Pat. No. 5,548,491) and for reflective lamps to yield a high color rendering (U.S. Pat. No. 4,315,186). For example in U.S. Pat. No. 5,548,491, issued to Karpen, discloses a motor vehicle headlight, either an incandescent lamp or a tungsten-halogen lamp comprising glass bulbs produced from neodymium doped soda lime glass and borosilicate or quartz glass, respectively. Neodymium oxide in the range of 5-30% by weight is disclosed therein. Hirano et al. (U.S. Pat. No. 4,315,186) disclose a reflective incandescent display lamp with a front lens section fused to a reflective mirror section, the front lens section formed from a Nd2O3 glass (preferably borosilicate as the base glass), the Nd2O3 accounting for 0.5-5% by weight.
Another important rare-earth spectrum modifying element is cerium. One important use of cerium oxide incorporation in glasses is an increase in photo-darkening resistance when these glasses are exposed to ionizing radiation. (See, S. Stroud, J. S., xe2x80x9cColor Centers in a Cerium-Containing Silicate Glassxe2x80x9d, J. Chem. Phys., 37 No. 4, pages 836-841, August 1962. The contents of which are incorporated herein by reference.) More important, cerium is the only rare-earth element that absorbs UV radiation while exhibiting no absorption in the visible region of the spectrum. (Weyl, Woldemar A, Coloured Glasses, pp. 220, 229, 230.) Therefore, cerium has value as a UV absorbing element when it is incorporated in a parent glass.
Traditionally, cerium has been used in combination with other rare-earth elements for decolorising glasses. G. P. Drossbach patented a mixture of neodymium and cerium oxide for decolorization of glasses. U.S. Pat. Nos. 3,865,747 (Greenberg) and 3,929,440 (Oldfield) disclose laser glasses containing neodymium and cerium. U.S. Pat. No. 3,685,747 (Greenberg) discloses that CeO2 in the range of 0.01-20 wt. % is added to ensure that uranium, another element in the glass composition, remains in its most fully oxidized state during the melting process; Nd2O3 in the range of 0.01-30 wt. % is disclosed. U.S. Pat. No. 3,929,440 (Oldfield) discloses a lithium silicate laser glass containing neodymium and cerium; CeO2 in the range of 0-0.1 wt. % is added as a solarization agent; Nd2O3 in the range of 2.5-6.5 wt. % is disclosed. U.S. Pat. Nos. 4,376,829 (Daiku), 4,390,637 (Daiku) and 4,521,524 (Yamashita) disclose glasses containing neodymium and cerium in combination for use in cathode ray tubes. U.S. Pat. No. 4,376,829 (Daiku) discloses a glass which absorbs in the yellow and blue regions of the spectrum for use in light-source cathode ray tubes; Nd2O3 in the range of 1-10 wt. % and CeO2 in the range of 0.1-3 wt. % are disclosed. U.S. Pat. No. 4,390,637 (Daiku) discloses an X-ray absorbing and non-discoloring glass for use in color cathode ray tubes, said glass containing Nd2O3 in the range of 0.1-5 wt. % and CeO2 in the range of 0-3 wt. %. U.S. Pat. No. 4,521,524 (Yamashita) discloses a glass filter for a CRT display, said glass containing Nd2O3 in the range of 5-40 wt. % and CeO2 in the range of 0-6 wt. %; CeO2 added as a coloring agent.
It would be highly desirable to combine the benefits provided by the characteristic absorption spectra of neodymium, i.e., absorption of light in the yellow region of the visible spectrum, and cerium, i.e., absorption of UV radiation with no visible light absorption, into a family of glasses that are suitable for employment as lamp envelopes, more particularly envelopes for high-temperature lamps (i.e., tungsten-halogen lamps), as well as sealed beam incandescent headlight lamps, whereby light sources of this type would emit minimum UV radiation and provide improved illumination in the surrounding environment. It is the basic purpose of the present invention to provide this desirable combination.
The present invention resides in a family of glasses that absorbs UV radiation and filter yellow light in the visible region of the electromagnetic spectrum, the glass composition consisting essentially, in terms of weight percent on the oxide basis, of: 55-95.7% SiO2, 0-28% B2O3, 0.5-18% Al2O3, 0-4% SrO, 0-13% BaO, 0-13% CaO, 0-8% MgO, 0-7.5% Na2O, 0-9.5% K2O, 0-1.5% Li2O, 0-1.5% Sb2O3, 0.4-4.5% Nd2O3, and 0.1-1% CeO2. The glasses of the present invention have a light transmission of greater than about 70 percent throughout visible wavelength other than yellow light.
Glasses of the present invention are capable of employment as lamp envelopes and sleeves. More particularly, the glasses can be formed into envelopes or sleeves for tungsten-halogen lamps and other high temperature light sources, as well as envelopes for sealed-beam incandescent headlights. Such lighting elements can be used within projection lighting systems, automotive lighting, or interior lighting devices.
The glasses of the present invention having a composition consisting essentially, in terms of weight percent on the oxide basis of: 90.5-95.7% SiO2, 2.8-3.0% B2O3, 0.7-1.7% Al2O3, 0.4-4.5% Nd2O3, and 0.1-1% CeO2 are suitable as envelopes for tungsten-halogen lamps and other high temperature lamps, as are glasses having a composition consisting essentially, in terms of weight percent on the oxide basis of: 55-66% SiO2, 0-13% B2O3, 14-18% Al2O3, 0-13% BaO, 0-4 SrO, 0-13% CaO, 0-8% MgO, 0.4-4.5% Nd2O3, and 0.1-1% CeO2.
The glasses of the present invention having a composition consisting essentially, in terms of weight percent on the oxide basis of: 64-85% SiO2, 11-28% B2O3, 0.5-8.5% Al2O3, 0-3.5% BaO, 0-1.5% CaO, 0-7.5% Na2O, 0-9.5% K2O, 0-1.5% Li2O, 0-1.5% Sb2O3, 0.4-4.5% Nd2O3, and 0.1-1% CeO2 are suitable as envelopes for sealed-beam incandescent headlights.
The glasses of the present invention also can be use for other applications where high contrast and enhanced visible properties of transmitted or reflected visible light can be a benefit. Such uses include, for example, opthalmic glass for eyewear, such as sunglasses, or as glass hosts for lasers. Similarly, the glasses can be made into computer screens with enhanced contrast properties can lessen visual discomfort, or rear-view mirrors to reduce glare.